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Investments (Portion of Unrealized Gains and Losses Relates to Equity Securities) (Detail) - USD ($) $ in Millions | 3 Months Ended | 9 Months Ended
--- | --- | ---
Sep. 30, 2018 | Sep. 30, 2018
Investment Holdings [Line Items] |  |
Net gains recognized during the period | $ 243 | $ 267
Less: Net gains recognized during the period on securities sold during the period | (7) | (42)
Unrealized gains (losses) recognized during the period on securities still held at September 30, 2018 | 236 | 225
Virginia Electric and Power Company |  |
Investment Holdings [Line Items] |  |
Net gains recognized during the period | 106 | 118
Less: Net gains recognized during the period on securities sold during the period | (3) | (26)
Unrealized gains (losses) recognized during the period on securities still held at September 30, 2018 | $ 103 | $ 92

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- Definition Amount of realized gain from sale of investment in equity security measured at fair value with change in fair value recognized in net income (FV-NI). + References Reference 1: http://www.xbrl.org/2003/role/disclosureRef -Publisher FASB -Name Accounting Standards Codification -Topic 321 -SubTopic 10 -Section 50 -Paragraph 4 -URI http://asc.fasb.org/extlink&oid=84241550&loc=SL75117546-209714 + Details
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- Definition Amount of unrealized gain (loss) on investment in equity security measured at fair value with change in fair value recognized in net income (FV-NI). + References Reference 1: http://www.xbrl.org/2009/role/commonPracticeRef -Publisher FASB -Name Accounting Standards Codification -Topic 321 -SubTopic 10 -Section 50 -Paragraph 4 -URI http://asc.fasb.org/extlink&oid=84241550&loc=SL75117546-209714 + Details
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